Actually, type annotations in Julia do not improve performance (and in some pathological cases can even reduce performance). The Julia JIT compiler will always

Actually, type annotations in Julia do not improve performance (and in some pathological cases can even reduce performance). The Julia JIT compiler will always infer the type at compile-time regardless of annotation and will (almost) always produce the optimal code. The reason for type annotations are for the multiple dispatch (multimethods), documentation, to deliberately restrict the polymorphism of a function and for the rare times when the compiler will not be able to infer the best type.